21

Figure 19.

The monitoring of a positive and negative supply voltage

The circuit shown in Figure 19. demonstrates the monitoring of a positive and a negative supply voltage. The device

 monitors the positive supply voltage and generates the system Reset. The delay time of device  thus depends

on the switch on times of the circuit being monitored. The device

ô must only inform device  of the failure of the

negative supply voltage. For this purpose, the RESET output of device

ô is connected to the gate of the JFET

BC264C.

As long as device

ô supplies a RESET signal, the transistor Q will remain conducting, and there will be a Low level

at the input

RESIN of device

. Only when the negative supply voltage has reached its nominal value and transistor

Q has thus become non conducting will the

RESIN input connected to it be pulled to High, and the delay time of

device

 commence. After this, the system will be switched into an active state.