This is a 100W DC servo amplifier circuit using a power mos tube. If you need a DC amplifier circuit, you can refer to it directly.
The DC servo amplifier circuit uses MOSFET 2SJ162 + 2SK1058 or MOSFET 2SK134 + 2SJ49 (To-3).
The output power of the speaker is 112 W at 8Ω and requires a power supply of +56V/-56V 4A/Ch.
I. Working principle of 100W DC servo amplifier circuit using power mos tube
The specific circuit diagram is shown below, and you may see that the characteristics of the DC servo amplifier circuit are similar to those of an operational amplifier power supply circuit.
The positive input of this circuit is used for signal input and the negative input is used to connect the feedback signal. (Image enlargement is recommended)
DC servo power amplifier circuit diagram using MOSFETs (scalable)
Here is a brief definition of a DC amplifier circuit first: The circuit can operate normally even at low frequencies similar to DC signals.
DC amplifier circuits can also be applied to servo amplifiers.
1.Gain and output power
The gain of the DC servo amplifier circuit depends on R8/R7, and the amplification 22 is calculated from each value in the circuit.
If the input signal size is 1V, the output voltage is 22V.
According to Ohm’s law, the power output can be calculated to be equal to
Power = (ExE)/R = 22 x 22 / 8 = 66.5 W with a load of 8 Ω or = 120 W with a load of 4 Ω
If you want to output 100 W at a load of 8 Ω, you need to input an input signal of not less than 1.28 V.
2.Adjust the idle current
Transistor Q5 is a constant current circuit, as the output mos tube bias, can be adjusted by adjusting VR1 to make the circuit stability better, VR1 should be carefully selected.
3.Protect mos tube
The gate of the power mos tube has a voltage regulator diode to prevent the mos tube from being damaged by an input signal higher than 14 V.
4.Prevent mos overload
When overload, the temperature of mos tube is higher and the resistance of mos tube is higher (in normal transistor, the resistance will be lower), so the current through mos tube will be lower.
If you install the right size heat sink, you can easily short the output and make sure the mos tube will not be damaged.
5.mos tube amplifier power supply
The most important factor in maximizing the potential of the circuit is the power supply circuit, and it is recommended to use a separate power supply for each amplifier.
The figure below shows a 56V 5A DC dual power supply circuit.
The advantage of this power supply is that it also helps reduce crosstalk and low frequencies, and then the transformer is able to provide more than 3A of current at the secondary coil (5A recommended) and voltage output at the 40V center.
The figure below shows a 56V 5A DC dual power supply circuit.
56V 5A DC Dual Power Supply Circuit (Scalable)
II. how to build a DC servo amplifier circuit?
1、0.5W resistor, tolerance: 1%
R1：56K
R2, R5: 3.9K
R3: 47K
R4：1K
R7：22K
R9：100Ω
R10：12K
R11, R12：100Ω
R13, R14：220Ω
R8, R21：10Ω 1W
Resistor components list (click to enlarge)
2、Capacitor
Ceramic capacitor C2：47pF 50V
Ceramic capacitor C10, C11: 27pF 50V
MKT or MKP capacitor C5：0.0056uF 100V
MKT or MKP capacitor C7：0.01uF 50V
MKT or MKP capacitor C8, C9: 0.1uF 100V
Electrolytic capacitor C1：10µF 25V
Electrolytic capacitor C4：47uF 50V
Electrolytic capacitor C3：100uF 50V
Capacitor components list (enlargeable)
3、Transistor Capacitor
PNP TO-92 transistors Q1, Q2: 2SA1016 or A872, -100V 50mA
PNP TO-92MOD transistor Q3, Q4: 2SD666, 80V 50mA
PNP TO-92 Transistor Q5: 2SB646, -80V 50mA
N-Channel Low Frequency MOSFET Q6: 2SK1058 ( To-3P) or 2SK134 (To-3)
P-Channel Low Frequency MOSFET Q7: 2SJ162 (To-3P) or 2SK49 (To-3)
Diodes D1, D2, D3: 1N4002, 100V 1A
Voltage regulator diodes D4, D5 : 12V 1W
4、Other
PCBs, transformers, power supply circuits, etc.
To build these circuits, simply install the components and lay them out correctly, remembering to look at the pinout of the components in the circuit first.
One thing that needs special attention is to install the mos tube on the heat sink and never short it to the heat sink.
This project needs to use the speaker protection circuit, otherwise, the speaker may be damaged.
Component pin arrangement
III. Setting and adjustment of DC servo amplifier circuit
When you are sure that the circuit is normal, connect the circuit to the power supply without connecting the speaker.
Next, use a voltmeter to measure the voltage of the speaker, which must be no voltage or zero voltage.
DC servo amplifier circuit setting and adjustment (amplification)
IV. DC servo amplifier circuit welding
The most important thing is welding.
When the output voltage is zero, the next step is to adjust the idle current of the current, connect the ammeter to the positive pole, and adjust VR1 to only 35mA.
DC servo amplifier circuit welding (amplification)
V. Attention points of DC servo amplifier circuit
- Installation of ground wire
It is installed in a metal box, just like a typical high power amplifier circuit. If the ground wire is installed incorrectly, it is easy to cause oscillation.
- Input and output circuits connected low
For the grounding of input and output circuits, we should separate the line from the ground at the same point. For the PCB of the circuit, the input and output ground are ingeniously separated. Moreover, the ground wire, especially the output and power supply, uses a large and durable power supply of more than 15A.
We can use AC input and DC input as required, but in general, it is recommended that AC input is safer.
