MIC5014/5015

Micrel

1997

5-143

5

Typical Applications

Variable Supply Low Side Driver for Motor Speed Control

(Figure 6) The internal regulation in the MIC5014/15 allows

a steady gate enhancement to be supplied while the

MIC5014/15 supply varies from 5V to 30V, without damaging

the internal gate to source zener clamp. This allows the speed

of the DC motor shown to be varied by varying the supply

voltage.

Figure 6: DC Motor Speed Control/Driver

Solenoid Valve Driver (Figure 7) High power solenoid valves

are used in many industrial applications requiring the timed

dispensing of chemicals or gases. When the solenoid is

activated, the valve opens (or closes), releasing (or stopping)

fluid flow. A solenoid valve, like all inductive loads, has a

considerable “kickback” voltage when turned off, as current

cannot change instantaneously through an inductor. In most

applications, it is acceptable to allow this voltage to momen-

tarily turn the MOSFET back on as a way of dissipating the

inductor’s current. However, if this occurs when driving a

solenoid valve with a fast switching speed, chemicals or

gases may be inadvertantly be dispensed at the wrong time

with possibly disasterous consequences. Also, too large of

a kickback voltage (as is found in larger solenoids) can

damage the MIC5014 or the power FET by forcing the Source

node below ground (the MIC5014 can be driven up to 20V

below ground before this happens). A catch diode has been

included in this design to provide an alternate route for the

inductive kickback current to flow. The 5k

Ω resistor in series

with this diode has been included to set the recovery time of

the solenoid valve.

Figure 7: Solenoid Valve Driver

MIC5014

OFF

ON

1

2

3

4

8

7

6

5

IRF540

NC

Gate

Gnd

Source

Input

V+

NC

NC

M

MIC5015

ON

OFF

1

2

3

4

8

7

6

5

IRFZ40

24V

NC

Gate

Gnd

Source

Input

V+

NC

NC

5k

Ω

1N4005

ASCO

8320A

Solenoid

Figure 5. High Side Driver with Delayed Overcurrent Shutdown

MIC5014

1

2

3

4

8

7

6

5

NC

Gate

Gnd

Source

Input

V+

NC

NC

10µF

R4

1k

Ω

R

S

0.06

Ω

12V

On

R1

1k

Ω

R2

120k

Ω

LM301A

2.2k

Ω

0.01µF

LM3905N

1

2

3

4

8

7

6

5

Logic

V+

Gnd

R/C

V

REF

Trigger

Emit

Coll

12V

1000pF

1k

Ω