Hello,
I'm trying to reverse engineer an electronic board that controls a brush motor.
I came up with this schematic after working with the board for a while.
The U2 mosfet controls the pump (motor) using typical Source Follower.
But the U1 mosfet, I don't know what function it has in this circuit, I don't understand its operation in this circuit.
Could any of you help me understand this circuit.
Thank you so much
What is VCC?
I don´t think "MCU" really goes directly to an MCU pin. Please confirm.
What exact type is D1?
D2 is drawn as a Schottky ... but maybe it is a zener? Please confirm.
What kind of pump is it? DC-Motor, vibration .. anything else?
Hi,
Thanks for answering, I clarify the circuit a little more.
- MCU does not really go to the U2 gate, I put it this way to simplify. The U2 gate is connected to a Driver and from the Driver to the MCU. The U2 has a zener between the Gate and the source. But this part of the circuit is easy to understand, what I don't understand is U2.
- Vcc is 12V.
- D1 is MBRB1045G Schottky
- D2 is Zener
- It is an engine of a car's ABS system.
If the extracted schematic is so far correct, D1 + U1 work as switchable freewheeling diode. U1 on = motor voltage is clamped to -0.3 V, U1 off = motor voltage can swing to negative voltage (fast discharge of stored inductor energy). To allow negative swing, U2 driver most be isolated.
I have no idea why the function is needed, we'd need more application details.
The schematic is well extracted (I reviewed it many times), but the only thing I can't find is where the U1 Gate is activated.
The diagram is the control of the ABS motor of a car.
On all the plates of these ABS systems there is not always the U1, only in some models.