Text preview for : MM101_Main_Power_Suppy_A2D95EE613B2C3CEE0339DFEEACCC3CE_25.pdf part of RCA D52130 Large File 6 pare RAR Folder containing: Flow Charts, Tech Tips, Trouble Shooting Manuals, Updates, Module Training, and Symptom Fixes
Back to : RCA_CTC210-211_01.rar | Home
28
Main Power Supply Most ground connections on the MM101 series chassis are cold, ( ), indicating they are isolated from the AC line. However, there are many "Hot" connections, ( ), meaning direct connection to the AC line. The AC input and primary side of the main and standby supply circuitry are examples. The main power supply output device, Q14100, heatsink is at AC line potential! Always use an isolation transformer when performing service on this chassis and other chassis in this family! Main Power Supply Overview The MM101 uses a version of the same ZVS supply as seen in the standby supply circuits. Instead of using the flyback portion of the waveform, it uses the forward mode to generate secondary current. This means it provides energy to the secondary during the forward conduction interval of the output device as the induction fields (flux lines) are expanding instead of when they are contracting. Previously, inductors were required on each winding to sustain the flux flow, but in this design, the windings in the primary circuit provide this function. A simple proportional self-oscillating drive circuit controls the on-off cycle of the output device, eliminating the need for an IC regulator. Proportional (linear) drive is required to maintain a relatively constant ratio of base current to collector current. This constant ratio prevents the switching transistor base from being overdriven in the forward direction during low current demands. Proportional drive also provides increased base drive when high peak current is required to ensure the output is driven to proper saturation, minimizing power dissipation in the device. The main supply operates at a higher frequency (80-120kHz) than the standby supply and supplies nearly 100% of the 450 watt peak requirements of the MM101. Isolation between the hot and cold portions of the supply are provided. Raw B+ Raw B+ is supplied from the same circuitry as the standby supply. Overcurrent and inrush current protection react equally to both supplies.
J14201 C14203 680PF 1KV
SERVICING PRECAUTION!
Variable IsoTap
Monitor ADD
AC Voltage Out with 120VAC In
EY14108
120 VAC 60 Hz
F14200 6A 125V
L14203
L14200
L14201
To Degaussing
CR14201
RAW B+
C14202
C14200
EY14107
C14208 680PF 1KV
C14205 0.012uF 250V
+
C14207 1000uF 200V
+12Vr
From Incoming AC Line
Figure 3-1,
Raw B+ Generation
Main Power Supply
29
Raw B+
Cold Ground Hot Ground
RESONANT INDUCTOR L14103
+15Vr
+12Vr
-15Vr DRIVE TRANSFORMER T14101
ON\OFF Q14105 FROM MICRO
OPTO-ISOLATOR U14102
CONTROL (Latch) Q14101/3
POWER OUTPUT Q14100
OUTPUT POWER TRANSFORMER T14100
+24Vr
+31.5Vr
OPTO-ISOLATOR U14100
OVER-CURRENT OVER-VOLTAGE R14100 & R14106
+76Vr
REGULATOR U14101
Figure 3-2, Main Supply Output Voltages Main Power Supply Block Diagram The main supply is capable of approximatedly 450 watts of peak power. All low voltage run supplies except +5V are generated by the main supply. The voltages generated are: l +15 volts l 15 volts l +24 volts l +31.5 volts l +76 volts These supplies are generated from Raw B+ from the incoming AC line. An inductor is used to smooth the incoming Raw B+. A current transformer is then inserted in series with the collector of the transistor power output device. The secondary of the current transformer then provides drive for the output transistor. By using a current transformer to couple the drive signal, drive current is proportional to the output current. This simplifies regulation, resulting in lower parts count providing an opportunity for greater reliability. Protection is provided against excessive power dissipation in the power output stages. Current and voltage are both monitored, but by different means. Excess current through the output device is monitored by resistors R14100 & R14106. The +76Vr supply is monitored by U14101 to regulate the main supply. Because the power output device and its control circuitry are connected to hot ground and output overvoltage is monitored from the cold ground run supplies, an opto-isolator is used to isolate the two grounds from each other.
30
Main Power Supply
Negative "Hot" Supply
-5Vr-Hot C14121 0.1uF 63V CR14117 C14104 0.1uF 63V
RAW_B+
L14103 9 2
CR14115 CR14128 6 T14101 10 1
On/Off
5 RAW B+ 4 1 CR14105 3.3V Q14100 T14100
R14103 33K
R14105 47K 1W
CR14104 R14114 330
FB14101
Control Latch
Q14101 Q14103
C14103 4.7UF 50V
C14113 0.0127 1600V JW14119
CR14120 Q14106 -5Vr-Hot
On/Off From Micro via Q14105 Run: +12V Standby: 0V
R14122 10
1
U14102
4
+76Vr
+15Vr R14116 220 1W 1 U14100 R14102 2000 2
RAW B+ 2 R14115 33K 3W 4 C14112 0.15uF 63V 3 R14138 47 3
R14119 100 1/2W R14118 5100 R14120 330 CR14108 CR14122
R14109 26.7K 1%
CR14107 C14120 1200uF 16V
R14117 2
CR14121 4.7V
R14101 200 R14111 866 1%
3 1 2 R14107 1 U14101
R14100 0.82 3W
R14106 0.39 3W
-5Vr-Hot
Drive
Figure 3-3, Main Supply
Feedback/Regulation
The main supply, like the standby, may be broken into smaller sections in order to understand its operation. These sections are: l l l l l l Drive Control (Latch Circuit) Negative "Hot" Supply Feedback/Regulation Output (Figure 3-4) On/Off
Main Power Supply
CR14110 T14100 16 C14105 5600uF 35V +24Vr
31
19 22
CR14103 +76Vr C14106 4700uF 80V C14111 470UF 80V
Output
-15Vr
15 CR14129 13
+15Vr CR14112 20 12 C14107 2200uF 35V JW14606 JW14101 R144136 6.2 +15Vr
JW14605 JW14607 U14104 +12VREG C14127 180uF 16V +12Vr
18 17 CR14113 14 JW14116 R14104 1800 2W
C14108 2200uF 35V
JW14107
+31.5Vr AUDIO
JW14123 JW14121 JW14122 AUDIO RETURN
Figure 3-4,
Main Supply, Secondary Run Supply Voltages
Unlike the standby supply which runs any time AC is present, the main supply must be turned on and off by the microprocessor. An additional on/off circuit interfaces with the microprocessor to provide this function. Main supply operation can be broken down into three parts: l Startup l Run l Regulation
When output transistor Q14100 fails, it is recommended to also replace latch transistors, Q14101 & Q14103. Unexpected excessive current may damage these transistors and other components in the immediate area.
TECH TIP
32
Main Power Supply Main Power Supply Drive Q14100 supplies all output transformer current. In addition, the same current is connected through a smaller, linear transformer, T14101, that generates two different supply voltages for use by the main supply. The first is a negative bias supply for the components in the main supply. It is normally labeled "-5Vr" for convenience and identification only. The supply is rarely exactly -5V. It will be discussed in more detail later. The second supply is for the drive circuit of Q14100. To start up, Q14100 is turned on by Raw B+. Once the supply completes the first "on" cycle, T14101 begins supplying a positive bias current for the base drive of the output device to continue operation of the supply. T14101 is very linear in its operation and also has its secondary and primary windings in phase. This means as current increases in the primary, it increases linearly and exactly in phase in the secondary. This establishes a proportional drive system that becomes self-oscillating. When Q14100 is turned on, current increases from common through T14100, T14101 and L14103 to Raw B+. As primary current increases, induced current in the secondary of T14100 also increases, establishing the run supplies from the secondary of the output transformer, T14100. Current is also increasing in T14101. CR14115 passes the positive portion of the current flowing in the T14101 secondary. As this current flows to the base of Q14100, C14103 is charged to a positive voltage. CR14105 limits the voltage across C14103 to about 3.3 volts.
RAW B+ -5Vr-Hot Bias Supply C14121 .1uF 63V L14103 9 CR14117 C14104 0.1uF 63V CR14115 CR14128 6 T14101 1 2
Positive Bias Supply
10
5 4
CR14105 3.3V Q14100 On\Off "Output" From Latch C14103 4.7uF 50V
1 T14100
C14113 0.0127 1600V
R14100 0.82 3W
R14106 0.39 3W
Figure 3-5, Main Power Output Current
Main Power Supply The waveform in Figure 3-5 shows the voltage on Q14100-C. Since there is no standby mode for the run supply this will be the only waveform. The frequency of this chassis settles out about 107kHz at 480 Vp-p depending upon the +76Vr load. The duty cycle is at 50% and varies little under load. When Q14100 shuts off, L14103 continues current flow, resonating with C14113, then reversing direction. As current flow in the primaries of T14100 & T14101 stops, some reverse voltage is induced into the secondaries. The secondary side diodes and Q14100 bias diodes are placed to block any induced current. CR14117 in the secondary of T14101 is biased to produce a negative supply to the main power supply circuitry. The negative supply is used to bias the control latch and regulation circuitry.
33
RAW B+ -5Vr-Hot Bias Supply C14121 .1uF 63V
L14103 9 2
CR14117 C14104 0.1uF 63V CR14115 CR14128 6 T14101 1
Secondary Reverse Current Flow for the Negative Supply
Positive Bias Supply
10
5 4
CR14105 3.3V Q14100 On\Off "Output" From Latch C14103 4.7uF 50V
1 T14100
C14113 0.0127 1600V
R14100 0.82 3W
R14106 0.39 3W
Figure 3-6, Main Power Output Current (Repeated)
34
Main Power Supply Control Latch The main supply uses a control latch similar to the standby supply. Q14101 and Q14103 make up a discrete latch that controls the conduction of the output device. The standby state has Raw B+ supplying power. System control holds Q14101-B low, resulting in Q14101 being held on. This turns Q14103 on and the two latch in the "on" condition. With the latch active, Q14101-E is low. Q14100-B is held low and it cannot conduct. The supply is off. As long as Q14101-B is held low, it stays off, keeping drive from the output device Q14100 and the supply will not run. Upon receiving an "On" command from System Control, Q14101-B is switched high and it shuts off. Raw B+ now supplies current to Q14100-B from R14103 and C14103/ CR14105 and the output device turns on. As current flows through Q14100 the supply begins generating output current. As long as Q14103-B remains low, and there is a "Run" command from the micro (holding Q14101-B high), the output device will conduct. When Q14100 output current increases far enough, the voltage drop of the emitter resistors R14100/06 generate a high enough voltage to turn on Q14103. When it turns on, its collector is pulled low. This turns on Q14101, pulling its emitter low. Since the output of the control latch is applied to Q14100-B, the low shuts off Q14100 output current, stopping run supply output transformer current. As output current through Q14100 drops, the voltage drop across R14100/06 also drops. When the voltage drops far enough, (and as long as system control is still supplying a high "Run" command), Q14103 turns off and the high from system control is again applied to the base of Q14101, which shuts off. Q14100-B goes high from voltage now supplied by T14101. This process continues indefinitely, unless other circuits interact with the two inputs of From T14101 the latch. Run: High
Stdby: 0 volts RAW B+ CR14105 3.3V R14103 33K Q14100 C14103 4.7UF 50V To Output Transformer T14100
R14114 330 In from Micro Run: High Stby: Low Q14103
FB14101 Q14101
R14120 330
CR14108
Q14101-B Stdby Run Run
Q14103-B xx High Lo
Q14103 xx On Off
Q14101 On On Off
Q14101-E Lo Lo High
Q14100 Off
CR14107 R14117 2
Off On
R14100 0.82 3W R14106 0.39 3W
Figure 3-7, Control Latch Circuit & Truth Table
Main Power Supply
35
Control Latch Operation The control switches act similar to an SCR, but with a few variations. Figure 3-8 shows a truth table for the main supply control latch shown in Figure 3-7. Again, while other ZVS supplies may have slight variations, the basic concept and operation is the same. The need to pay particular attention to the switching states is critical! The main power supply contains a control latch operating very similar to the standby supply latch with a notable exception. The control latch for the main supply consists of Q14103 and Q10101. There is a main control signal from the microprocessor on Q14101-B. It is high, about 5V during run and low during standby. Figure 3-8 is a simplified diagram of the main supply control latch. Notice the similarity with the standby supply latch. The latch not so much turns the output device on and off as it simply "allows" the positive bias to turn it on. The rest of the time the latch "holds" the bias off the output. IN1 in this case is the microprocessor signal. It is high during run and low during standby. By looking at the truth table when IN1 is low, the output will always be low because a low resistance path to ground exists when Q2 is on. No matter what IN2 is, the output will remain low. When the main supply switches on, IN1 is high shutting off Q2. The positive bias supply is now on the output. Also, IN2 is now able to control the latch output. If IN2 is high, Q1 turns on, turning on Q2 and the low impedance path to ground is again established, removing the positive bias supply from the output. The output device would now be off. If IN2 is low, Q1 turns off, Q2 turns off and the positive bias supply is now available on the output device turning it on.
B+ Positive Bias Supply
TECH TIP
R5 33K OUT R1 330 IN1 Q1 R4 330 IN2 CR2 CR1 R3 2 IN1 Q2 A B C D 0 0 1 1 IN2 0 1 0 1 OUT 0 0 1 0
Figure 3-8, Digital Latch & Truth Table
36
Main Power Supply Negative Hot Ground Supply A negative run supply using hot ground is developed when the main supply is operating. It is used to provide a "trip" voltage reference for the output device shutoff, essentially raising and lowering the DC bias of the control latch. When transformer T14101 is in flyback mode, flux fields are collapsing and current is induced such that CR14117 conducts, creating a nominal 5V supply across filter capacitor C14121. Ground return for T14101 is through Q14100 emitter current limiter resistors, R14100/06. The supply is allowed to fluctuate depending upon the load on the main supply. As the supply load increases, more current is drawn through the primary of T14100 and T14101, increasing current in both secondary supplies. As current increases, the output voltage of the secondary of T14101 increases and the output voltage at CR14117 goes more negative. If primary current decreases, secondary current in T14101 also decreases and the output voltage of CR14117 decreases, going toward 0V. The key to the operation of the negative supply is to remember that shortly after startup, it reaches a nominal level, normally around -5V. It then varies (in normal operation) towards -9V. CR14121 is a protection zener diode limiting the maximum negative voltage to around -5V. With the zener, any large changes in the negative supply amount to smaller changes at the junction of R14119 and CR14121. The negative supply does not directly affect the regulation of main power! However, it is used elsewhere as a bias voltage. Also note that as the negative supply increases (towards -9V), the waveform from the emitter of Q14100 is also increasing, so the bias relationship is not quite as simple as this representation. Another bias supply called the +5Vr-Hot for convenience is very similar. It is used to provide a base bias supply for the output device, Q14100 during normal operation.
RAW B+ -5Vr-Hot C14121 0.1uF 63V -5Vr-Hot R14119 100 1/2W CR14117 +5Vr-Hot CR14115 6 T14101 1 L14103 9 2
10 R14120 330
R14118 5100
5 4
CR14108 1 T14100
C14120 100uF 16V
CR14121 4.7V
R14117 2
R14100 0.82 3W
R14106 0.39 3W
Figure 3-9, Negative Hot Ground Supply
Main Power Supply Internal Overcurrent Protection The main supply is internally protected against over current by sampling the output device current. Current through Q14100 generates a voltage drop across resistors R14100/06. This voltage is coupled to Q14103-B of the control latch via R14120. When the voltage reaches a limit determined by the bias voltages, the latch trips, shutting off Q14100 base drive by reducing the positive bias supply, stopping output current. When the voltage across R14100/06 drops far enough, the latch turns off and base drive is allowed to return to Q14100. As base drive returns, current in the output transformer begins to increase.
From T14101 Run: High Stdby: 0 volts RAW B+ CR14105 3.3V R14103 33K Q14100 C14103 4.7UF 50V To Output Transformer T14100
37
R14114 330 In from Micro Run: High Stby: Low Q14103
FB14101 Q14101
R14120 330
CR14108
CR14107
R14117 2
R14100 0.82 3W
R14106 0.39 3W
Figure 3-10, Overvoltage/Overcurrent Protection Main Supply On-Off The interface between the microprocessor and the main supply allowing on/off control of the supply is very simple. During standby, the on/off signal from System Control, U13101-4, is high, turning Q14105 on. This places the anode of the LED portion of U14102 (pin 1) at or near 0 volts, shutting off the output portion and current flow. When the microprocessor receives a turn-on command, U13101-4 is pulled low, shutting off Q14105. The +12V standby supply now pulls current through U14102 LED which turns on the output portion allowing current flow. Normal voltage drop in the output portion of U14102 is approximately 0.20.5 volts.
+12Vs +12Vs RAW B+ R14105 47K 1W
[R14131] 68K OFF/ON FROM SYSTEM CONTROL ON (RUN): Low OFF (Stdby): High [R14132] 1000
[R14133] 2200
JW14102
RUN: +12V STNDBY: 0V
1 U14102 C14114 .01UF R14121 6800 Q14105 2 R14118 5100 R14120 330 R14100 0.82
4
RUN: ~+0.3V STNDBY: ~+1.4V
3
R14106 0.039
Figure 3-11, MM101 Main Supply On-Off
38
Main Power Supply Main Supply Start-up The first cycle of supply operation was covered in the section titled "Main Power Supply Output Transformer". To understand the main power supply startup, it is important to understand the supply voltages and operation during standby. When the microprocessor is maintaining an "off" state, U14102 is off and the 5Vr Hot supply is zero volts. Q14106 is biased on by a current path from Raw B+ to hot ground via R14105, R14118, R14120, R14100/06. With Q14106 on, a current path exists from Raw B+ to ground via R14103, R14114, CR14120, Q14106-E/C and the remainder of the path from Q14106-E to hot ground. This places a low voltage on the Q14101-B, (with respect to Q14101-E), turning it on. When Q14101 is on, a low output is held on the base of the output transistor, Q14100. This removes base drive and the output is held off indefinitely.
RAW B+ L14103 9 2
6 T14101 10 5 RAW B+ CR14105 3.3V R14103 33K Q14100 4 1
1
T14100
R14105 47K 1W
CR14104 R14114 330
FB14101
C14103 4.7UF 50V
C14113 0.012 1600V
Q14101
CR14120 Q14106 On/Off From Micro via Q14105 Run: +12V Standby: 0V -5Vr-Hot Q14103
1 U14102
4
R14119 100 1/2W R14118 5100 R14120 330 CR14108 R14117 2
2
3
CR14107 C14120 1200UF 16V
CR14121 4.7V
R14100 0.82 3W
R14106 0.39 3W
Figure 3-12, MM101 Main Supply Turn On At startup, the micro sends a turn-on signal which ultimately turns on the opto-isolator output. When the output of the opto-isolator is active, it does not allow enough bias voltage for Q14106 to remain active and it shuts off. With no current path, Q14101-B now goes high (>+2.0V), and Q14101 turns off. As Q14101 turns off, the positive bias supply now appears on Q14101-E allowing base bias to turn on the output transistor, Q14100 and the conduction cycle begins.
Main Power Supply A current path now forms from Raw B+ through R14103, CR14105, Q14100-E/B and R14100/06 to hot ground, and the output transistor, Q14100 begins to conduct. This initial "tickle" current begins the output transistor conduction cycle. Positive bias for continued output conduction is provided by a second transformer, T14101, whose primary is in series with the output transistor, Q14100 and output transformer, T14100. The current is rectified by CR14115 to provide conduction bias voltage for the base of Q14100. During the current buildup cycle, this voltage increases, increasing the bias on Q14100, driving it harder into conduction. The bias voltage will continue to increase until something happens to shut off output current. In normal operation the bias supply reaches a nominal level and remains there as long as the supply runs. Once current through the primary of T14101 is cutoff, collapsing fields induce current in the secondary in the opposite direction. During this swing of the secondary, current through CR14117 generates a negative supply. CR14128 serves as part of the return path during this cycle similar to a damper diode.
RAW B+ L14103 9 C14121 0.1uF 63V CR14117 C14104 0.1uF 63V CR14115 CR14128 6 T14101 10 RAW B+ Positive Bias Supply 5 4 1 CR14105 3.3V Q14100 T14100 1 2 -5Vr-Hot
39
Negative Bias Supply
R14103 33K
R14105 47K 1W
CR14104 R14114 330
FB14101
C14103 4.7uF 50V
C14113 0.012 1600V JW14119
Q14101
CR14120 Q14106 On/Off From Micro via Q14105 Run: +12V Standby: 0V -5Vr-Hot Q14103
R14122 10
1 U14102
4
R14119 100 1/2W R14118 5100 R14120 330 CR14108 CR14122
2
3
CR14107 C14120 1200uF 16V
R14117 2
CR14121 4.7V
R14100 0.82 3W
R14106 0.39 3W
Figure 3-13, MM101 Main Supply (Primary Side)
40
Main Power Supply Main Supply Operation C14103 eventually charges to the zener voltage of CR14115 and clamps. Output current through Q14100 during this charge time continues to rise. Several other things are happening at the same time. As current flows through Q14100, it also flows through the output transformer T14100 and secondary "hot supply" transformer T14101. T14101 primary and secondary are in phase, so the polarity is transferred directly. As current begins to flow in the secondary, it begins to supply the base bias voltage for Q14100 through CR14115. As output current rises, the voltage across R14100/06 increases, eventually triggering a latch circuit consisting of Q14101 & Q14103 (Discussed previously in section "Logic Latch"). Q14103 turns on, turning on Q14101, closing a current path that in effect removes base current from Q14100. The negative bias built on C14103 with respect to the positive voltage on the emitter is required for fast turn-off of output transistor, Q14100.
RAW B+ -5Vr-Hot C14121 0.1uF 63V CR14117 C14104 0.1uF 63V CR14115 CR14128 6 T14101 10 RAW B+ Positive Bias Supply 5 4 1 CR14105 3.3V Q14100 T14100 1 L14103 9 2
Negative Bias Supply
R14103 33K
R14105 47K 1W
CR14104 R14114 330
FB14101
C14103 4.7uF 50V
C14113 0.012 1600V JW14119
Q14101
CR14120 Q14106 On/Off From Micro via Q14105 Run: +12V Standby: 0V -5Vr-Hot Q14103
R14122 10
1 U14102
4
R14119 100 1/2W R14118 5100 R14120 330 CR14108 CR14122
2
3
CR14107 C14120 1200uF 16V
R14117 2
CR14121 4.7V
R14100 0.82 3W
R14106 0.39 3W
Figure 3-14, Main Supply Initial Conduction Cycle
Main Power Supply Output Current Shutoff As Q14100 shuts off, C14113 now begins to conduct and current flow through T14100 and T14101 decreases. As the flux fields collapse, reverse current in T14101 induces a negative voltage in the secondary winding, reversing its current flow. CR14115 now shuts off and the reverse voltage on C14103 holds CR14105 off. Complete current shutoff in the output transistor, Q14100, and the output transformer is now assured by the negative voltage coupled from T14101 through C14104, C14103 and CR14105.
41
RAW B+ -5Vr-Hot C14121 0.1uF 63V CR14117 C14104 0.1uF 63V CR14115 CR14128
L14103 9 2
Negative Bias Supply
6 T14101 10
1
RAW B+
Positive Bias Supply
5 4 1 CR14105 3.3V Q14100 T14100
R14103 33K
R14105 47K 1W
CR14104 R14114 330
FB14101
C14103 4.7uF 50V
C14113 0.012 1600V JW14119
Q14101
CR14120 Q14106 On/Off From Micro via Q14105 Run: +12V Standby: 0V -5Vr-Hot Q14103
R14122 10
1 U14102
4
R14119 100 1/2W R14118 5100 R14120 330 CR14108 CR14122
2
3
CR14107 C14120 1200uF 16V
R14117 2
CR14121 4.7V
R14100 0.82 3W
R14106 0.39 3W
Figure 3-15, Main Supply Output Shut off
42
Main Power Supply Main Supply, Return to Conduction Cycle As the reverse current through T14100 passes back through zero, the voltage drop across R14100/06 also drops, removing the bias on the latch, Q14101/03. When the latch turns off, base current through Q14100 is again allowed through R14103 and CR14105 using a bias voltage developed from the secondary winding of T14101 and CR14115. The process now begins again. As long as the microprocessor continues to supply an "on" signal, (placing a "high" on the input of the latch at Q14101-B) the supply will continue to run indefinitely. It is by design self-oscillating. However, there are parameters the supply must stay within for normal operation.
RAW B+ -5Vr-Hot C14121 0.1uF 63V CR14117 C14104 0.1uF 63V CR14115 CR14128
L14103 9 2
Negative Bias Supply
6 T14101 10
1
RAW B+
Positive Bias Supply
5 4 1 CR14105 3.3V Q14100 T14100
R14103 33K
R14105 47K 1W
CR14104 R14114 330
FB14101
C14103 4.7uF 50V
C14113 0.012 1600V JW14119
Q14101
CR14120 Q14106 On/Off From Micro via Q14105 Run: +12V Standby: 0V -5Vr-Hot Q14103
R14122 10
1 U14102
4
R14119 100 1/2W R14118 5100 R14120 330 CR14108 CR14122
2
3
CR14107 C14120 1200uF 16V
R14117 2
CR14121 4.7V
R14100 0.82 3W
R14106 0.39 3W
Figure 3-16, Main Supply Output Turn-on
Main Power Supply Run Supplies The main power supply in the MM101 generates several different supplies. They are: l l l l l +76 +31.5 +24 +15 +12
43
All are generated from the secondary winding of the main supply transformer, T14100. In addition, the run supplies are regulated and monitored for overload conditions by monitoring the +76V supply. To do this, the cold grounded run supplies must be isolated from the hot ground supply current generator circuits. Run Supply Generation Run supply generation is straightforward. As current is conducted through the primary winding of T14100, it is mirrored in the secondary. Diode polarity is appropriately observed to generate the proper voltage source. All devices are discrete with the exception of the +12V regulator. It is a TO220 package regulator mounted on a heat sink. CR14110
T14100 16 C14105 5600uF 35V +24Vr
19 22
CR14103 +76Vr C14106 4700uF 80V C14111 470UF 80V
15 CR14129 13 -15Vr +15Vr CR14112 20 12 C14107 2200uF 35V JW14606 JW14101 R144136 6.2 +15Vr
JW14605 JW14607 U14104 +12VREG C14127 180uF 16V +12Vr
18 17 CR14113 14 JW14116 R14104 1800 2W
C14108 2200uF 35V
JW14107
+31.5Vr AUDIO
JW14123 JW14121 JW14122 AUDIO RETURN
Figure 3-17, Run Supplies
44
Main Power Supply Main Supply Voltage Regulation Only the +76V run supply voltage is directly monitored by the main supply generator to provide regulation for all other run supplies. Since the run supplies are connected to cold ground and the supply generation circuitry uses hot ground, they must be isolated from each other by an opto-isolator. This makes monitoring slightly more difficult. The regulator works by varying the voltage on the emitter of the first latch transistor, Q14103. If there were no regulator voltage, the trip voltage of Q14103 would be determined by the voltage drops of CR14107 & the emitter/base voltage drop of Q14103.
TECH TIP
The actual trip voltage of Q14103 is lower than might be expected for two reasons. First, CR14107 is a low-IR Schottky diode, normally dropping only 0.3V. Also, the -5Vr supply discussed previously normally lowers the trip voltage towards zero volts. The nominal voltage expected at the base of Q14103 is 0.31.2 volts.
U14100 is an opto-isolator, and U14101 is another voltage comparator with an internal reference of +2.5 volts. If the voltage at pin 1 is greater than +2.5, the internal resistance between pins 2 and 3 is very low. If the voltage on pin 1 is less than +2.5, the internal resistance approaches infinity. It operates as a high gain comparator with a gate of +2.5 volts. The +76Vr supply is connected to a voltage divider network consisting of R14109, R14111 and R14101. R14101 is adjusted to place +2.5 volts on pin 1 of U14101 during normal operation. (NOTE: The +76Vr supply may change depending upon CRT size. Consult the appropriate Service Data for specifications on the chassis version.) If the +76V supply rises, the voltage on U14101-1 also rises and the impedance between pins 2 and 3 decreases. The opto-isolator, U14100 now turns on reducing the voltage on pin To T14100 4 towards the negative supply. RAW B+
Output Transformer R14103 33K Q14100
R14114 330
Q14101 R14120 470 CR14108
+76Vr
+15Vr R14116 220 1W 1
RAW B+ R14115 33K 3W 4 U14100
Q14103
R14117 2 C14112 0.27uF
R14109 26.7K 1%
R14102 2000 2 3 R14138 47
CR14107
R14100 0.82 3W
R14106 0.39 3W
R14101 200 R14111 866 C14117 1% 0.1uF
3 1 2
R14107 1 R14112 1
U14101
-5Vr-Hot
Figure 3-18, Main Supply Regulation
Main Power Supply If the output load increases, output voltage decreases. When the sampled voltage on pin 1 of U14101 drops below +2.5, current through U14101 and the LED portion of U14100 is reduced to zero. Current flow in the transistor side of U14101 now shuts off and the voltage on U14100-4 increases. Since this is the same as the emitter of Q14103, it also increases. As the voltage on Q14103-E increases, it takes more voltage on Q14103-B to "trip" the latch circuit. The conduction cycle of the output device will be correspondingly longer, providing more output power for the secondary supplies, eventually raising the output voltage until it reaches the new setpoint. For example, during normal operation, U14100 transistor side (pins 3 and 4), would be on and there would be little (or very low) voltage on pin 4. The supply would reach a nominal operating state based on the load of the run supplies. If the load on the +76Vr supply increases, it would normally begin to drop. When the sampled voltage on U14101-1 begins to drop below +2.5V, current flow to the LED portion of U14100 stops, and output current (U14100/3-4) also shuts off. C14112 is now allowed to charge between ground and Raw B+, reaching a maximum of about +0.3V before CR14107 "clamps" the voltage. As the voltage on Q14103-E rises, the voltage on Q14103-B must be higher in order to trip the latch and stop output device drive. This means the output will be on longer developing more output current and increasing available power to the run supplies in an attempt to increase run supply voltage. On the other hand, if output voltage is too high, U14101-1 begins rising above +2.5V and it turns on. The internal resistance of the device decrease allowing current flow. The LED portion of U14100 now turns on, allowing output current (U14100/3-4) flow. C14112 is now charges between ground and the negative supply. As the voltage on Q14103-E decreases, the voltage on Q14103-B is lower and the latch stops output device drive at a lower current draw. This means the output will not be on as long, developing less output current and decreasing available power to the run supplies in an attempt to reduce run supply voltage. The regulator is extremely linear, constantly switching on and off when the sample voltage is too high and too low. This means the opto-isolator, U14100 is constantly "rocking" the bias voltage on the emitter of Q14103 between +0.3V and the negative bias supply.
45